Tunable inductors are useful for fine-tuning/adjusting various circuit designs. One area where tunable inductors provide such benefits involves VCO (voltage controlled oscillator) circuit design, and in particular, advanced SerDes (serializer/deserializer) circuit designs. In such advanced SerDes circuit designs, inductance values are especially small and operating frequencies typically operate at frequencies of 10 GHz and above. Because of the nature of such circuit designs, accurate modeling of inductors becomes particularly challenging due to the unpredictable effects caused by the circuit environment (e.g., uncertainty in returning path formed from other circuit elements).
Whenever the operating frequency of the circuit falls outside of the desirable range, modifications must be made to the circuit in order to tune the circuit back within the desirable range. Such modifications typically involve modifying the design of particular circuit elements including inductors. Modifying the design of particular circuit elements results in changes to the circuit floorplan, which requires significant redesign of the entire circuit. Prior approaches have involved substituting circuit elements with alternative circuit elements in order to achieve such fine tuning. These approaches suffer from the requirement of significant circuit redesign and time-consuming layout changes.